The present invention relates to the field of cathode ray tube manufacture. More particularly, the present invention relates to the process of cleaning cathode ray tube funnels before an interior coating is applied. The present invention provides an improved chemical wash that is gentler on the washing equipment, easier to dispose of and provides as thorough a cleansing of the funnel as previous washes at a significant cost savings.
BACKGROUND OF THE INVENTION
Cathode ray tubes (xe2x80x9cCRTsxe2x80x9d) are used in most television sets and computer and video monitors. A typical CRT is illustrated in FIG. 1. The CRT (100) is a glass tube with a bottle-like shape in which a relatively flat bottom portion (101) narrows into an elongated neck portion (102). The relatively flat portion (101) of the CRT (100) becomes the screen on which the display of the television set or monitor is generated when the CRT is incorporated therein. An electro-luminescent material, such as phosphorus, that emits light when struck by an electron beam, is coated over the interior of the screen portion (101) of the CRT (100).
An electron gun (not shown) is then installed in the neck (102) of the CRT (100). A stream of electrons emitted from the electron gun is scanned over the electro-luminescent layer and turned on and off during the scanning to cause the electro-luminescent layer to glow in certain places and not others. In very simple terms, this is how an image is generated on the screen of a television or video monitor. A yoke (not shown) is provided around the neck (102) of the CRT (100). This yoke produces a changing magnetic field through which the electron beam from the electron gun passes. The electron beam is deflected by the magnetic field of the yoke. Consequently, by varying the magnetic field created by the yoke in a precise cycle, the electron beam can be scanned, line-by-line, over the entire surface of the screen to generate video images thereon.
A cathode ray tube is generally constructed in the following matter. The neck (102) or funnel portion of the CRT (100) is formed open at both ends. Then the relatively flat display portion (101) is sealed to the large end of the funnel and the electron gun is installed in the narrow end or neck of the funnel.
The display portion (101) is sealed to the funnel (102) using frit. Frit is a glass paste that can be cured or hardened. Frit (103), in paste form, is applied around the large end of the funnel (102) between the funnel (102) and the display portion (101). The frit is the cured or hardened to form a frit seal (103) between the funnel (102) and the display portion (101).
Before the funnel (102) and display (101) portions are sealed, a coating is applied to the interior of the funnel (102). This coating includes carbon material necessary to the optimal operation of the CRT (100). FIG. 2 illustrates a portion of a CRT production line in which the carbon material coating is applied to the interior of the funnel (102).
As shown in FIG. 2, cathode ray tube funnels (102) are supported during processing on holders or pallets (200). The pallets (200) include a base (201) with supports (202) that hold the funnel (102) in an upright position with the open, large end of the funnel (102) pointing upward. The pallets (200) carrying the funnels (102) may be transported on a conveyor (203).
First, each funnel (102) is brought to the coating application station (205). At the coating application station (205), the coating of carbon material is sprayed into the interior of the funnel (102). A spray head (204) sprays the coating into the open interior of the funnel (102) as the funnel (102) is supported on the pallet (200). Then, the funnel (102) is conveyed into and through a drying oven (206) to dry the newly applied coating.
As noted above, prior to applying the interior coating, the funnel is open at both ends. In particular, the large end of the funnel is open to receive the interior coating before being sealed with a display portion. Consequently, contaminants, such as dust, particulate matter, chemical residues, moisture, etc., can be introduced to and lodge in the open funnels. If this contamination remains when the interior coating is applied inside the funnel, the contamination will degrade both the quality and longevity of the interior coating and the finished CRT.
For these reasons, it is conventional practice to wash each funnel with a chemical wash before the interior coating is applied. This washing is intended to remove all contaminants from the interior of the funnel so that the interior coating can be cleanly and effectively applied.
In the past, ammonium bifloride has been used in the chemical wash for cleansing CRT funnels prior to the application of the interior coating. While ammonium bifloride does an adequate job cleansing the funnel, the ammonium bifloride is also very hard on the equipment used to wash and clean the funnels.
For example, the cleansing wash is typically sprayed from a nozzle or sprayer into the open CRT funnel to clean the funnel. However, the ammonium bifloride tends to clog the sprayer, thereby decreasing the amount of wash delivered to cleanse the funnel. This can obviously result in an incomplete cleansing of the funnel as well as costing time and expense spent to maintain the sprayers in minimal operating condition.
Additionally, the chemical wash containing ammonium bifloride cannot be released as waste until it has been treated to render it safe. Thus, there is an additional expense incurred to treat the waste from an ammonium bifloride washing system before the wastewater can be released into the sewer system.
Consequently, there is a need in the art for an improved method and system of washing cathode ray tube funnels prior to applying interior coatings to those funnels.
The present invention meets the above-described needs and others. Specifically, the present invention provides an improved method and system of washing cathode ray tube funnels prior to applying interior coatings to those funnels.
Additional advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The advantages of the invention may be achieved through the means recited in the attached claims.
The present invention may be embodied and described as a method of cleansing a funnel of a cathode ray tube prior to application of a carbon material coating on an interior of the funnel by washing the cathode ray tube funnel with an aqueous solution of trisodium phosphate. This method preferably includes preparing the aqueous solution of trisodium phosphate by mixing water and trisodium phosphate.
Preferably, the water is heated prior to the mixing of the water and the trisodium phosphate. The mixing of the water and the trisodium phosphate is preferably performed automatically by connecting the output of a water heater with a supply of trisodium phosphate.
The washing of the cathode ray tube funnel with an aqueous solution of trisodium phosphate further is preferably performed by spraying the aqueous solution of trisodium phosphate into the cathode ray tube funnel. The method also preferably includes draining the aqueous solution of trisodium phosphate from the washing chamber where the washing of the cathode ray tube funnel is performed, and may include discarding the aqueous solution of trisodium phosphate without further chemical treatment of the aqueous solution.
After the washing phase, the method of the present invention may include drying the cathode ray tube funnel. The drying of the cathode ray tube is preferably performed by heating air and blowing the heated air on the cathode ray tube funnel to dry the funnel. The method may also include extracting the heated air from the washing chamber in which the washing of the cathode ray tube funnel was performed to facilitate the drying process.
The present invention also encompasses a system or apparatus for performing the method described above. More specifically, the present invention may be embodied in a system for cleansing a funnel of a cathode ray tube prior to application of a carbon material coating on an interior of the funnel. This system would preferably include a washing chamber containing the funnel of the cathode ray tube; and an aqueous solution of trisodium phosphate supplied into the washing chamber to wash the funnel of the cathode ray tube.
This system may also preferably include a supply line for supplying the aqueous solution of trisodium phosphate to the washing chamber; a metered supply of trisodium phosphate connected to the supply line; and a water line connected to the supply line. The water line may preferably include a water heater.
To wash the funnel, the system preferably includes a sprayer connected to the supply line for spraying the aqueous solution on the funnel. A drain system may be provided for draining the aqueous solution of trisodium phosphate from the washing chamber.
A drying system may be connected to or incorporated in the washing chamber for drying the cathode ray tube funnel following the washing of the cathode ray tube funnel with the aqueous solution of trisodium phosphate. The drying system preferably includes a heater/blower unit for heating air and blowing heated air into the washing chamber to dry the funnel. The drying system also preferably includes an exhaust system for exhausting the heated air from the washing chamber.